1. Field of the Invention
The present invention relates to a maintenance and inspection system for a printing machine, and more particularly, the present invention relates to a system for determining times and the extent of appropriate maintenance measures based on various conditions and variables.
2. Description of the Related Art
Printing machines, and in particular sheet-fed offset printing machines, have a large number of individual parts which have a limited lifetime or service life. Furthermore, specific operating media and consumable materials have to be replaced or renewed from time to time.
In the case of sheet-fed offset printing machines, the number of parts which are subject to wear is particularly high, because of the complexity of the sheet transport. The elements of the separating and traction suckers in the feeder, which are usually made of rubber, wear as a function of the type of printing materials transported, since rough paper reduces the tightness of the seal of the suction elements. The conveyor belts of the conveying table which performs the sheet transport between the feeder stack and the feed of the printing machine wear because they interact with the printing material, and also because of the tension necessary for their operation. Furthermore, components made of rubber or elastomers are prone to become hardened and break, depending on the time in use. As a result, such rubber or elastomer elements have to be replaced after specific times, irrespective of stress imposed thereon.
The grippers or gripper pads which perform sheet transport within and between the individual printing units are also subject to wear. This wear depends on the roughness of the printing materials being transported, and also on the number of sheet transports carried out and on the printing speed. Worn sheet grippers or gripper pads are recognizable by sheet transfers which cause register differences. Register differences of this type then have to be compensated for by time-consuming adjustment operations of the register of the printing units following such sheet transfers. During register correction operations of this type, reject prints are produced. The replacement of worn grippers or gripper pads and their adjustment is a time-consuming procedure which causes long downtimes of the machine.
There are also additional parts which become and materials which are consumed. For example, such additional parts and materials of a sheet-fed offset printing machine include rubber blankets in the individual printing units, lubricants in the gears of the main and of the secondary drives, the tips of metering elements which interact with rotating rolls, the lubricants, in particular for the gripper mechanisms, and also lubricants for other moving parts in the cylinders and the transfer and driving belts such as toothed and V belts.
In order to avoid production failures which are caused by the sudden failure of such parts, and the resultant relatively long downtimes of the machine during production, it is necessary for the printing machine and its corresponding elements to be maintained regularly so that worn elements are replaced and consumable materials replenished regularly. Because of the large number of elements subject to wear, as well as the varying service lives of various elements and consumable materials (depending on the time or the operation cycle), machine manufacturers, in conjunction with the manufacturers of the respective components, define maintenance intervals which have to be complied with unconditionally. However, even strict compliance with the maintenance intervals and the implementation of the replacement or repair measures required is no guarantee against sudden production failures. The reason for this is in the wear relationship between specific elements and the type of production carried out, for example, the type of printing materials used, the inks used for printing and further production conditions (printing speed, frequency. of printing interruptions and the like).
The necessary maintenance intervals for specific elements (for example V belts or toothed belts) can also be lengthened considerably, given regular monitoring of specific parameters and their correction. The regular monitoring of the tension of a toothed belt/V belt increases the service life thereof so that the time when a time-consuming replacement operation is performed can be delayed considerably. The quality of consumable materials, such as the gear oil or the rubber blankets in the individual printing units, for example, also has a significant effect on the necessary maintenance and inspection intervals of the corresponding components. The use of a cheap but lower-quality oil, in conjunction with the production conditions during its use, under certain circumstances makes more frequent oil changing necessary than the use of a higher quality lubricant. In this case, the type of rubber blankets used has a strong dependence on the type of printing materials used.
In order to cope with the above-described difficulties, maintenance and inspection systems used in motor vehicles are considered. In such systems, the frequency of the maintenance work to be carried out (inspection intervals) is determined from sensor data from the engine, the gearbox, the chassis and the bodywork, in conjunction with prescribed data. The necessary inspection intervals are thus not only fixedly related to the time or the mileage but also as a function of the stress prevailing during the operation of the vehicle. It is therefore possible for an inspection interval defined to be distinctly longer as a result of frequent travel over long distances and under not too high a stress than is the case over frequent short journeys over the same number of miles, which stress the material more significantly. However, these maintenance and inspection systems take no account at all of the planned purposes for which the vehicle will be used in the future.
In the case of printing machines, it is known to monitor specific components additionally for wear or consumption. Examples of this are monitoring the level of containers providing operating materials, such as oil supply, damping solution, ink, powder and the like. Furthermore, in printing machines, it is known to monitor the temperature of cylinder bearings by using sensors, since an abnormal temperature/time behavior is indicative of anticipated damage. It is also possible for the tension of V-belt drives to be monitored by recording the slippage and an appropriate error signal is generated if the slippage values are too high.
Monitoring and diagnostic systems are also known in the field of printing machine electronics. Using an additional sensor system, for example, the degree of wear of contacts (brushes) of the commutators of DC motors can be monitored. In this case, however, error signals are only generated when the contacts/brushes have worn beyond a specific extent. Preventive maintenance measures cannot be generated by such a system.
In order to provide the gripper systems on the rotating cylinders with lubricant, it is necessary to open guard elements on the machine (folding catwalks, sliding guards and the like), and to move the machine into a specific position by moving in very small increments. Movement of the machine to the specific position is achieved by a machine control system generating specific control commands and feeding these control commands to the main drive of the machine. If the printing machine has a rotary encoder (absolute rotary encoder, incremental encoder), it is also possible to require permanently programmed (maintenance) positions, which are moved to automatically when triggered manually.
In particular, moving automatically to specific positions makes it easier for the operating personnel to carry out the appropriate work, but the operating personnel must comply strictly with the sequence of the individual operations, in order to avoid damage to the machine as a result of collision between moving parts and so on. When carrying out adjustment work, it is also necessary to carry out specific operations in a predefined order one after another. If damage to the machine occurs, then it is often not possible to determine the cause or the triggering event, since it is not possible to rule out that the operating or maintenance personnel have not carried out the corresponding maintenance work in accordance with the instructions or required sequence of operations.
In the case of maintenance work which requires performance of a large number of steps, it is also not possible to rule out specific operations being carried out in a working sequence which differs from that required, since specific machine positions (moving to the position) are omitted as a result. The operating or maintenance personnel are often not aware that, although the same machine position has been assumed, a maintenance operation necessitating a different machine position must have been carried out previously. Missing moving operations for machine positions in this way, and thus changing the operating sequence, can likewise not be detected subsequently, so that if faults or damage to the machine occur, the cause cannot be established, and any repair/fault correction measures which arise are very complicated.
DE 43 27 848 C2 discloses a monitoring device for a printing machine in which the signals from individual limit switches/sensors or other signal transmitters of guard elements/emergency-off push-buttons are evaluated in conjunction with the rotational speed of cylinder achieved by the drive of the printing machine. When the guards are open, the machine must run only at a maximum possible permissible rotational speed, which is determined by the monitoring device recording the signals from the sensors, limit switches and push-buttons. This monitoring device also generates the maximum possible permissible rotational speed. If it is established that there is a difference between the current rotational speed of the machine (of the drive) which is actually run and the highest possible permissible rotational speed determined by the monitoring device, then the drive is brought to a standstill and an electromagnetically operated brake is applied. However, this monitoring device does not permit the subsequent implementation of maintenance work.